In general, aqueous paints, adhesives, or pressure-sensitive adhesives are produced by using aqueous resins such as emulsion resins. When the resins are used for such applications, the resins are required to have an adequate degree of viscosity, and hence it is essential to use a viscosity modifier. As the viscosity modifier, there are known natural viscosity modifiers such as carboxymethylcellulose or hydroxyethylcellulose, alkali thickening-type viscosity modifiers, which are thickened with an alkali, such as polyacrylic acids or polyacrylic acid-containing copolymers, and urethane-type viscosity modifiers such as urethane-modified polyethers (see, for example, Patent Literatures 1 to 4).
In general, if a natural viscosity modifier or alkali thickening-type viscosity modifier out of those viscosity modifiers is added to an aqueous paint or the like, the paint has thixotropic viscosity and not leveling viscosity, and may have poor water resistance. On the other hand, a urethane-type viscosity modifier can provide a wide range of viscosities including thixotropic viscosity and leveling viscosity, and the paint has high water resistance. Because of these reasons, urethane-type viscosity modifiers are widely used for various applications or in various regions.
Many emulsion resins and paints each containing a viscosity modifier are transported, stored, and sold in cans or containers made of resins or the like. In many cases, the period between production of the paints or the like and actual use thereof may be long, and the paints or the like may often be exposed to high or low temperatures for long periods of time during transportation, storage, or the like. Specific examples thereof include storage in midsummer or in a very cold land and marine transportation right on the equator or in a very cold land. When an emulsion resin-based paint or the like containing the urethane-type viscosity modifier is exposed to a high-temperature or low-temperature state for a long period of time, there arises a problem where the product viscosity of the paint increases. This increase in product viscosity may inhibit fundamental properties of the paint to cause failures in painting or troubles in a coating to be obtained.